I got this too when i was in DFU mode and was trying to load the custom ipsw. What i did, as the guide said, is to
1. restart the computer.
2. Go into itunes, shift + click restore find the original ipsw that you downloaded, not the custom, the original
3. after thats done put the touch into DFU mode like in step 9, i believe, of the guide
4. shift + click on restore and load the custom ipsw.. the last step seems to take a looooong time so be patient..